New JW converts generally fall into 2 categories:
1. Those who are conned into believing JWs have ultimate Bible secrets. These typically burn out fast and are now less likely due to easy internet access. Those that last, drive the born-ins up a wall (which they can't admit). Most born-ins I know have a JW side that's paraded out when needed, but they're just like non-JWs when the pressure isn't on.
2. Those who seek support/benefits from an anyone-can-join group. They may
have even been 'discouraged' from other churches after attending for a
while. The JWs are a great way to get "insta-friends" if you can't get the real thing. I bet everyone can remember several "odd" people at their hall. Many born-ins just tolerate them for the sake of appearances/expectations.
The new converts are helping to drive out the born-ins.